b.Fatal("expected image to be opaque")
	}
	b.SetBytes(640 * 480 * 4)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		Encode(io.Discard, img)
	}
}

func BenchmarkEncodeNRGBA(b *testing.B) {
	img := image.NewNRGBA(image.Rect(0, 0, 640, 480))
	if img.Opaque() {
		b.Fatal("expected image not to be opaque")
	}
	b.SetBytes(640 * 480 * 4)
	b.ReportAllocs()
	b.ResetTimer()